Support procedures returning values

source/lexer.ll

@@ -100,6 +100,9 @@ or                      {
 not                     {
                             return yy::parser::make_NOT(this->location);
                         }
+return                  {
+                            return yy::parser::make_RETURN(this->location);
+                        }
 [A-Za-z_][A-Za-z0-9_]*  {
                             return yy::parser::make_IDENTIFIER(yytext, this->location);
                         }